Alloy steel and articles



atented Sept. 11, 1945 ALLOY STEEL AND ARTICLES Henry S. Schaufus,Baltimore, Md., assignor to Rustless Iron and Steel Corporation, acorporation of Delaware No Drawing. Application December 13, 19M),

Serial No. 370,072

8 Claims.

This invention relates to an alloy steel, and to articles of usefashioned of the same.

One of the objects of my invention is the provision of an alloy steelwhich not only is corrosion resistant, but which combines high impactstrength with good machinability.

Another object is the provision of such a steel which readily may beworked hot or cold without tearing, cracking or splitting, and whichreadily lends itself to various cutting, drilling, tapping, threadingand other machining operations, in the production of spindles, gears,worms, shafts, threaded bolts, pins, nuts, studs, discs, bushings,sleeves, rings, valve seats and the like.

A further object of my invention is the provision of machined articlesof the character described, which in spite of sharp notches andsections, nevertheless are strong, tough Wear-resistant and are of highimpact strength under the many conditions of heat, vibration, shock andthe like encountered in actual practical use.

Other objects of my invention will be obvious in part and in partpointed out hereinafter.

The invention consists in the combination of elements, mixture ofmaterials, and composition of ingredients .and in the relation of eachof the same to one or more of the others as described herein. the scopeof the useful application of which is indicated in the claims.

As conducive to a clear understanding of certain features of myinvention, it may be noted at this point that many types f alloy steelsare known and used at the present time. In the field of corrosionresisting steels which commonly are referred to as stainless steels,types are available for a wide variety of service requirements. At thepresent time there are some forty or fifty standard types available onthe market.

Several of the types of stainless steel now on the market find use asmachine parts or like applications where good machining qualities arenecessary. For example, the 12% to 14% chromium grade of stainless steelcontaining suflicient sulphur to lend the desired free machiningqualities to the steel, is useful in a variety of applications wheremild corrosive conditions are encountered. This steel is readilyworkable into bars, rods, wire, plate, sheet and strip throughconventional hot or hot and cold methods. The steel is ferritic ormartensitic, largely depending upon its carbon content, and may be heattreated to give agood range of hardness, strength, and impactresistance. The steel, however, is not qualified for applications inwhich a wide variety of corrosiveconditions are encountered, nor evenwhere severe corrosive conditions of a limited character are met with.

In applications where rather severe corrosive conditions are found,machine parts commonly are fashioned, for example, of the austeniticchromium-nickel stainless steel of the 18% chromium-8% nickel grade,including suflicient sulphur to give the desired free-machiningqualities. Such a steel is strong, ductile, tough and of good impactstrength. On the other hand, however, it is not hardenable by heattreatment and it is quite expensive.

It ordinarily might be expected that desired corrosion resistingproperties could be obtained in ferritic and martensitic stainless alloysteels of chromium contents substantially greater than the 12% to 14%chromium grade mentioned above. For example, it might be expected thatthe 17% chromium grade of free-machining stainless steel would be suitedfor machined parts and articles where reasonably severe corrosiveconditions are encountered. I find, however, that such a steel, althoughof good corrosion resistance and good machinability, is virtuallyworthless for such applications under the conditions of serviceencountered in actual practical use. Such articles and productsfashioned of v this steel are found to possess an exceedingly low impactresistance. The products are inclined to fail, particularly at thenotched, grooved or otherwise constricted sections.

One of the principal objects of my invention, therefore, is theprovision of a comparatively inexpensive stainiess alloy steel which isof good corrison resistance and good machinability, which may behardened by heat treatment and which is strong and tough, and whichpossesses a good impact strength, and which readily may be fashionedinto various articles and products having machined or otherwiseconstricted portions and yet which are adapted to withstand the variousconditions of shock, vibration and impact encountered in actual,practical use.

Referring now more particularly to the practice of my invention, Iprepare a stainless steel containing 14.5% to 18.0% chromium, 20% to 50%sulphur, .5% to 2.0% nickel, with a maximum carbon content of .20% andwith the remainder principally iron and the usual impurities. This steelis made by any one of several known steel melting processes sucn, forexample, as that generally described in the United States Letters Patent1.925,182, issued to Alexander L.

Feild on September 5, 1933, and entitled Process to the manufacture ofrustless iron; or United States Letters Patent 2,056,162 issued toWilliam B. Arness on October 6, 1936, and entitled Production ofrustless iron, from which it is obtained in ingot form. The sulphuraddition is made in conventional manner as through the addition of lumpsulphur to the ladle in tapping the melting furnace.

The steel is worked from ingots to billets or blooms, and thence tobars, rods and wire in the one case, or plate and sheet in the otherthrough conventional hot-working methods, although best results are hadwhere the working is conducted in the manner more particularly describedand claimed in my co-pending application, Serial No. 870,073, died ofeven date herewith and entitled Method of working alloy steel andproducts thereof. Where desired these converted products may be furtherfashioned into cold-rolled or colddrawn bars, rods and wire, orcold-rolled plate and sheet. Also, where desired certain of theconverted products may be forged or drop-forged to approximatespecifications of size and shape.

The various converted products are made into a host of articles or partsof articles of ultimate use where various cutting, drilling, tapping,threading or other machine operations are resorted to. For example, mystainless alloy steel is particularly suited to the manufacture ofspindles, gears, worms, shafts, threaded bolts, pins, nuts, studs.discs, bushings, sleeves, rings, valve seats and like articles or partof articles. I find that such articles are strong and tough. They areresistant to a wide variety of corrosive agents. Of particularimportance these articles possess great impact strength, a result whichis indeed surprising in view of their threaded. notched or otherwisesharply restricted sections. In a particular case, for example, where abar of steel according to my invention is found to possess an impactstrength of 25 to 100 foot-pounds Izod, this inversely depending uponthe carbon content, a like bar of free-machining stainless steel ofidentical chromium, sulphur and carbon contents, without the nickelcontent however, possesses an impact strength of only 1 to 5 foot-poundsIzod. The various articles and parts fashioned of my stainless steel arewell calculated to withstand the bending, torsion and impact stressesen-- countered in actual use.

The particular correlation of the ingredients chromium, nickel, sulphurand carbon according to my invention is pecially important in achievingthe desired combination of physical properties. I find that where theproportions given are substantially departed from, one or more of thedesiredproperties are lost. For example, with an increase in chromiumabove the limiting figure given the impact strength is lost; and with adecrease beyond its limit, the corrosion resistance accordinglydecreases. Similarly, for a decrease in nickel below its lower limitimpact suffers while for an increase above its upper limit thesteel isinclined to air-harden and crack. Likewise, there is a loss ofmachinability with a substantial lowering of the sulphur content belowits limiting .value and an attendant hot shortness and loss of impactstrength where it above .the limiting value.

Many of the desirable characteristics of my high impact, free-machiningstainless steel are achieved in the non-hardening or ferritic grades(these lncllldlni; those which harden to some slight extent) whilefurther desirable characteristics are had in the hardening ormartensitic grades. I find, for example, that excellent imis appreciablyincreased assases pact strength in combination with machinability andgood corrosion resistance are obtained in the non-hardening steelcomprising 14.5% to 16.5% chromium, 20% to .50% sulphur, .5% to 2.0%nickel, with a maximum carbon content of .1296 and the principal part ofthe remainder iron. Similarly, I find that desirably good impactstrength, good corrosion resistance and desired hardness are achieved inwhat I call the hardening grade comprising 14.5% to 18.0% chromium, 20%to .50% sulphur, .5% to 2.0% nickel, with .12% to .20% carbon and theremainder principally iron.

In my high impact, free-machining stainless steel, best results areachieved where the silicon content is no more than about .35% althoughwhere the nickel is on the high side and the chromium is on the lowside, the silicon content may amount to as much as .60%.

Also, in my sainless steel it frequently is desirable to employ a highmanganese content. I find that best results in impact strength,machinabllity and workability in the hot and cold conditions arerealized where the manganese content is used in amounts up to 1.5%, therange preferably being .5% to 1.5%. This quantity of manganese alsoassures a certain desired fluidity in the melting, tapping and teemingof the steel.

My high impact free-machining stainless steel also is benefited throughthe addition of the ingredient nitrogen in the amount of .06% to 30%.This ingredient readily may be introduced into the metal during itsmelting as described, for example. in the eo-pending application ofWilliam B. Amess, Serial No. 113,258, flied November 28, 1936, andentitled Production of rustless iron. Such a steel, in accordance withmy invention, then analyzes 14.5% to 18.0% chromium, .20% to .50%sulphur, .5% to 2.0% nickel, .08% to .30% nitrogen, with a maximumcarbon content of .20% and the remainder of the metal principally iron.It will be understood that the silicon and manganese contents preferablyare at a maximum of .60% for the silicon and up to 1.5% for themanganese. While in the hardening grade of my steel the nitrogen contentmay range from .06% to .30%, I prefer to maintain this ingredient atavalue of .06% to 20% in the non-hardening grade. One of the advantagesof including in my steel the prescribed amount of nitrogen is to assurea uniformly high impact strength in spite of vagaries in the hot-workingtemperatures employed, as is more particularly described and claimed inmy co-pending application, Serial No. 370,074, entitled alloy steelmethod and products,

filed of even date herewith.

A further improvement in strength, toughness and general corrosionresistance is had in my alloy steel by including in its composition asmall amount of molybdenum. For the hardening grade molybdenum isemployed in the amount of .2% to 2.0%. In the non-hardening grade themolybdenum content preferably is preserved beflow in grinding and tween.2% and 1.0%,, Molybdenum imparts a certain denseness to the metal andmoreover renders the steel peculiarly wear-resistant, a result which isparticularly important in the machine parts fashioned according to myinvention. Molybdenum also assures a good surface in machined articlesand products apparently giving these products a certain resistance tosurface polishing operations. This ingredient is gainfully employed inmy steel both where one or more of the ingredients silicon, manganeseand nitrogen are as specified above,

stantially all iron.

and where they are at values other than as specifled, it being notedhowever that best results are had in my steel and in the variousarticles and machine parts fashioned of the same where all of theingredients are present in the amounts indicated.

Thus, it will'be seen that there has been provided in this invention analloy steel and certain manufactures or articles fashioned of the same,in which the various objects hereinbefore noted, together with manythoroughly practical advan= tages, are successfully achieved. It will beseen that my alloy steel is strong, tough and corrosion resistant.Moreover, it will be seen that my steel possesses good impact strengthin combination with good machinability. "Furthermore, it will be seenthat these various properties are had at minimum expense and that thiscombination of ,useful properties is particularly important in variousmachined products and articles, especially machine parts, havinggrooved, slotted, notched or other constricted portions, which nor:

mally give rise to high impact stresses under the conditions of shockand vibration encountered in use.

As many possible embodiments may be made of my invention and as manychanges may be made in the embodimentshereinbefore set forth, it is tobe understood that all matter described herein is to be interpreted asbeing illustrative and not as a limitation.

I claim as my invention:

1. In compositions of matter of the c de= scribed, an alloy steel orgood corrosion resisting properties, good machining characteristics dgood resistanceto impact, said alloy steel comprisin 14.5% to 18.0%chromium, 20% to .50% sulphur, .5% to 2.0% nickel, .06% to 30% nitrogen,with a. maximum carbon content of 20%. and the remainder substantiallyall iron.

2. In compositions of matter of the class described, an alloy steel ofgood corrosion resisting properties, good machining characteristicsandgood resistance to impact, said alloy steel comprising 14.5% to 18.0%chromium. .20% to .50% sulphur, up to 1.5% manganese, .5% to 2.0%nickel, 06% to .30% nitrogen, with a maximum carbon content or 20%,

3. In compositions of matter of the class described, an alloy steel ofgood corrosion resisting properties, good machining characteristics andgood resistance to impact, said alloy steel comprising 14.5% to 18.0%chromium, 20% to .50% sulphur, .5%

gen, 9, maximum or 35% silicon, with a maximum to 2.0% nickel, .06% to30% nitroand the remainder subn 3 carbon content of 20%, and theremainder substantially all iron.

4. In compositions of matter of the class described, an alloy steel ofgood corrosion resisting properties, good machining characteristics andgood resistance to impact, said alloy steel comprising 14'.5% to 18.0%chromium, 20% to .50% sulphur, .5% to 2.0% nickel, .2% to 2.0%molybdenum, 06% to 30% nitrogen, a maximum of 20% carbon, and theremainder substantially all iron.

5. In manufactures of the class described, machined articles, such asspindles, gears, worms, shafts, axles, threaded bolts, pins, nuts andthe like, having threaded or notched portions, which articles ar strong,tough, corrosion resisting and of good impact strength, consisting ofalloy steel comprising 14.5% to 18.0% chromium, 20% to .50% sulphur, .5%to 2.0% nickel, 06% to 00% nitrogen, a maximum of 20% carbon, and theremainder substantially all iron.

6. In manufactures of the class described, machined articles, such asspindles, gears, worms, shafts, axles, threaded bolts, pins, nuts andthe like, having threaded or notched portions; which articles arestrong, tough, corrosion resisting and of good impact strength,consisting oi an alloy steel comprising 14.5% to 18.0% chromium, -20% to.50% sulphur, .2% to 2.0% molybdenum, .5% to 2.0% nickel, .06% to 30%nitrogen, a maximum of 35% silicon, a maximum of 20% carbon, and theremainder substantially all iron.

7. In manufactures of the class described, machined articles, such asspindles, gears, worms, shafts, axles, threaded bolts, pins, nuts andthe like, having threaded or notched portions, which articles arestrong, tough, corrosion resisting and of good impact strength,consisting of an alloy steel comprising 14.5% to 18.0% chromium, 20% to.50% sulphur, 2% :to 2.0% molybdenum, .5% to 2.0% nickel, 06% to .30%nitrogen, up to 1.5%

manganese, a maximum of .60% silicon, a' inaxi- 7 mum of .20% carbon,and the remainder substantially alliron.

8. In compositions of matter oi the class described, an alloy steel ofgood corrosion-resisting properties, good machining characteristics,good workability in the hot and cold conditions and good resistance toimpact, said alloy steel com- I prising 14.5% to 18.0% chromium, 20% to.50%

sulphur, .5% to 1.5% manganese, .5% to 2.0% nickel, 06% to 30% nitrogen,at maximum of .60% silicon, with a maximum carbon content 5 or 30%;, andthe remainder substantially all iron.

ma a. scnaonns.

